1. Field of the Invention
The present invention generally relates to a scroll compressor primarily used for a refrigerating apparatus, and more particularly to a scroll compressor comprising a first scroll, and second and third scrolls arranged on both sides of and associated with the first scroll so that two compression chambers are provided.
2. Description of the Prior Art
A conventional scroll compressor of this kind is disclosed in FIG. 9. As shown in FIG. 9, the conventional scroll compressor comprises a first scroll 102, a second scroll 103 and a third scroll 104. The first scroll 102 has a flat plate 121 and back and front spiral ridges 122a, 122b provided on both sides of the flat plate 121, respectively. The second scroll 103 has an end plate with a flat face 131 confronting one face of the flat plate 121, and a spiral ridge 132 provided on the flat face 131. Similarly, the third scroll 104 has an end plate with a flat face 141 confronting the other face of the flat plate 121 of the first scroll 102, and a spiral ridge 142 provided on the flat face 141. The second and third scrolls 103, 104 are arranged on both sides of the first scroll 102 in a manner to sandwich the first scroll 102 therebetween. Thus, the back spiral ridge 122a of the first scroll 102 and the spiral ridge 132 of the second scroll 103 are meshed with each other, while the front spiral ridge 122b of the first scroll 102 and the spiral ridge 142 of the third scroll 104 are meshed with each other. Suction ports 105, 105 are respectively formed in the vicinity of the external end portions of the back spiral ridge 122a of the first scroll 102 and the spiral ridge 132 of the second scroll 103 and in the vicinity of the external end portions of the front spiral ridge 122b of the first scroll 102 and the spiral ridge 142 of the third scroll 104. The suction ports 105 communicate with a suction space 106 in a casing 101 being a low-pressure dome. On the other hand, discharge ports 108, 108 are respectively formed in the vicinity of the internal end portions of the back spiral ridge 122a of the first scroll 102 and the spiral ridge 132 of the second scroll 103 and in the vicinity of the internal end portions of the front spiral ridge 122b of the first scroll 102 and the spiral ridge 142 of the third scroll 104. The discharge ports 108 communicate with a discharge passage 107. Compression portions 109, 109 are defined between the spiral ridges 122a and 132, 122b and 142. In this scroll compressor, a fluid taken in from the respective suction ports 105 and compressed at the respective compression portions 109 is joined at the discharge ports 108 and then discharged through the discharge passage 107 communicating with the discharge ports 108.
As described above, in the conventional scroll compressor, the suction and compression operation is effected on both sides of the first scroll 102. Therefore, a thrust load acting on the first scroll 102 is offset by the balance between fluid pressures at the compression chambers formed on both sides of the first scroll 102, so that a thrust load acting on a thrust bearing of the first scroll 102 can be reduced, resulting in reduction of loss at the thrust bearing. In addition, the capacity of the compressor can be increased.
However, since a fluid, which is in the suction space 106 in the casing 101 designed as a low-pressure dome, is taken in from the two suction ports 105 communicating with the suction space 106, and compressed at the two compression portions 109 in parallel and then discharged from the two discharge ports 108 to the discharge passage 107, the volumetric efficiency cannot be effectively increased. More specifically, since a vicinity zone of the external end portions of the spiral ridges 122a and 132 and that of the external end portions of the spiral ridges 122b, 142 are both placed in an atmosphere of a suction pressure, both of the compression portions 109 having completed the fluid suction and containment processes are necessarily adjacent to the suction space 106. As a result, as shown in FIG. 10, the fluid under compression in the two compression portions 109 leaks to the suction space 106 through clearances between end faces of the external end portions of the spiral ridges 122a, 122b of the first scroll 102 and the flat faces 131, 141 of the end plates of the second and third scrolls 103, 104, respectively. Since this leakage takes place on both sides of the first scroll 102, the volumetric efficiency decreases.